This application claims priority from U.S. provisional patent application Serial No. 60/151,029 filed Aug. 27, 1999, the entire disclosure of which is incorporated herein by reference.
The present invention relates to improved magnetic data/information recording, storage and retrieval media and to a method for manufacturing same. More specifically, the present invention relates to improved, high areal recording and storage density, patterned magnetic media and to a method for manufacturing same which can be readily practiced at a low cost comparable to that of conventional multi-grain magnetic media.
Magnetic media are widely utilized in various applications, particularly in the computer industry, and efforts are continually made with the aim or increasing the areal recording density, i.e., the bit density, or bits/unit area, of the magnetic media. Conventional magnetic thin-film media, wherein a fine-grained polycrystalline magnetic alloy layer serves as the active recording medium layer, are typically formed as xe2x80x9cperpendicularxe2x80x9d or xe2x80x9clongitudinalxe2x80x9d media, depending upon the direction of magnetization of the grains. In this regard, the xe2x80x9cperpendicularxe2x80x9d recording media have been found superior to the more common xe2x80x9clongitudinalxe2x80x9d media in achieving very high bit densities. However, as grain sizes decrease in order to achieve increased recording bit densities, e.g., to somewhere around 20 Gb/in2, effects ansing from thermal instability, such as xe2x80x9csuper-paramagnetismxe2x80x9d are encountered. One proposed solution to the problem of thermal instability with ultra-high recording density magnetic recording media is to increase the crystalline anisotropy, and thus the squareness of the bits, in order to compensate for the smaller grain sizes.
An alternative approach, however, to the formation of very high bit density magnetic recording media, is one which delays the onset of thermal instability problems by storing the data/information in isolated magnetic particles. In contrast with conventional polycrystalline-based magnetic media where thousands of very small-sized grains are required for storing a single data bit, so-called xe2x80x9cpatternedxe2x80x9d magnetic media utilize only a single, relatively large-sized particle for storage of a single data bit. For example, in xe2x80x9cpatternedxe2x80x9d media, the single particles (i.e., the basic storage unit) are more than about ten times larger than the thermally unstable grains of conventional very high recording density magnetic media, in principle permitting storage densities of about 100 Gb/in2 and above.
Analogous to the situation with conventional polycrystalline thin film magnetic media, both xe2x80x9clongitudinalxe2x80x9d and xe2x80x9cperpendicularxe2x80x9d types of patterned magnetic media have been developed, depending upon whether the magnetization direction of the particles is parallel or perpendicular to the media surface. When fabricated in disk form, such xe2x80x9cpatternedxe2x80x9d media are readily adapted for use in conventional hard drives, with most of the drive design features remaining the same. Thus, hard-drive based xe2x80x9cpatternedxe2x80x9d media technology would comprise a spinning disk with a slider head flying above it in closely-spaced relation thereto, with read sensors or a read/write head that magnetizes and/or detects the magnetic fields emanating from the magnetic particles.
To date, several approaches have been utilized for the formation of xe2x80x9cpatternedxe2x80x9d magnetic media, which approaches can be classified into two major categories, i.e., (1) mechanical or mechanical replication; and (2) lithographic patterning.
According to the first approach, as exemplified by the Atomic Force Microscopy (xe2x80x9cAFMxe2x80x9d) approach of IBM (B. Terris et al., Data Storage, August 1998, pp. 21-26), a sharp tip is utilized for scanning extremely close to the surface of a storage medium. The tip is located at the end of a flexible cantilever, which deflects in response to changes in the force imposed on the tip during scanning. The force may arise from a variety of effects, including, inter alia, magnetic force. To date, two types of AFM drives have been demonstrated, i.e., write-once/read-only and read-only. The former type of AFM drive, which provides write-once/read-only capability, utilizes a heated AFM tip for writing once by forming small indentations or pits in the surface of a substrate. e.g., of polycarbonate. Data is read by using the AFM tip to scan the thus-indented surface and sensing the changes in the force imposed on the AFM tip due to the presence of the indentations.
The latter type of AFM drive functions in a read-only mode, and data is initially written in the form of indentations (pits) which are created in the surface of a SiO2 master by means of an electron beam. The data, in the form of the indentations, is then transferred, by replication, to a photopolymer-coated glass substrate, which photopolymer is cured by exposure to ultra-violet (UV) radiation to thereby form a surface topography representing the data. The data is then read from the cured photopolymer surface by scanning with the AFM tip to sense the changes in force thereat due to the indentations.
According to the second, lithographic approach, thin film processes such as are utilized in the fabrication of semiconductor integrated circuits including micro-sized features are adapted for making high aspect ratio, single column/bit, perpendicularly patterned media. According to one particular approach (M. Todorovic et al., Data Storage, May 1999, pp. 17-20), designed to increase coercivity, hence stability, of the individual magnetic columns, electroplated nickel (Ni) is utilized for forming the columns, and gallium arsenide (GaAs) and alumina (Al2O3) are employed as embedding media for the columns. The fabrication process starts with an electrically conductive GaAs substrate, on which thin layers of aluminum arsenide (AlAs) and GaAs are successively deposited. Scanning electron-beam lithography is then utilized to define the magnet patterns on a resin-coated sample. The patterns in the e-beam exposed resin are developed utilizing an appropriate solvent system and then transferred, as by chemically-assisted ion beam etching (xe2x80x9cCAIBExe2x80x9d), into the AlAs/GaAs layers. After pattern definition, the AlAs layer is converted into Al2O3 by wet thermal oxidation. The thus-produced patterned layer acts as a mask for additional etching for extending the pattern of depressions perpendicularly into the GaAs substrate. The etched depressions in the Al2O3 substrate are then filled with electroplated Ni. Overplated Ni xe2x80x9cmushroomsxe2x80x9d are then removed, as by polishing, to create a smooth surface for accommodating slider contact therewith.
Thus, the overall process sequence for forming such media requires successive, diverse technology steps for (1) MBE growth and mask deposition; (2) electron beam lithography; (3) chemically assisted ion beam etching; (4) wet thermal oxidation; (5) chemically assisted ion beam etching; and (6) electroplating and polishing. The result is a complex and time-consuming fabrication process. Moreover, each of the above-described approaches for patterned media manufacture typically involves substantial capital investment for the process equipment, which together with the inherent process complexity, render them too costly for use in high product throughput, magnetic disk media manufacture.
Accordingly, there exists a need for improved, high bit density, patterned magnetic data/information recording, storage, and retrieval media, e.g., in hard disk form, and a method for manufacturing same, which can be implemented at a cost compatible with that of conventional, multi-grain disk media by primarily utilizing current media manufacturing methodologies, technologies, and instrumentalities.
The present invention, therefore, addresses and solves problems attendant upon patterned magnetic media manufacture, and affords rapid, cost-effective fabrication of high bit density, patterned magnetic media, e.g., in the form of hard disks, while providing substantially full compatibility with all mechanical and electrical aspects of conventional hard disk technology. Moreover, the patterned magnetic media of the present invention can be simply and reliably manufactured largely by means of conventional manufacturing techniques.
An advantage of the present invention is an improved method of manufacturing a high areal storage density, patterned magnetic data/information recording, storage and retrieval medium.
Another advantage of the present invention is an improved, high areal storage density, patterned magnetic data/information recording, storage and retrieval medium.
Additional advantages, aspects, and other features of the present invention will be set forth in the description which follows and in pant will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized and obtained as particularly pointed out in the appended claims.
According to an aspect of the present invention, the foregoing and other advantages are obtained in pant by a method of manufacturing a high areal storage density, patterned magnetic recording, storage and retrieval medium, which method comprises the sequential steps of:
(a) providing a non-magnetic substrate having a surface for layer formation thereon;
(b) forming a layer of an amorphous, paramagnetic or anti-paramagnetic material on the substrate surface, the layer of amorphous, paramagnetic or anti-paramagnetic material comprising at least one component which is ferromagnetic when in at least partially crystalline form; and
(c) at least partially crystallizing the at least one component of the layer of amorphous, paramagnetic or anti-paramagnetic material at selected locations thereof to thereby form a pattern of at least partially crystalline, ferromagnetic particles or grains of the at least one component of the layer, the ferromagnetic grains being spaced apart and surrounded by a matrix of the amorphous, paramagnetic or anti-paramagnetic material.
According to embodiments of the present invention, step (b) comprises forming as the amorphous, paramagnetic or anti-paramagnetic layer a metal glass layer including at least one metal element which is ferromagnetic when in at least partially crystallized form, e.g., the metal glass layer comprises at least one of iron (Fe), nickel (Ni), and cobalt (Co); and step (c) comprises at least partially crystallizing the at least one component of the amorphous, paramagnetic or anti-paramagnetic layer by increasing the temperature thereof at the selected locations, e.g., increasing the temperature at the selected locations up to at least a phase transition temperature of the at least one component.
According to further embodiments of the present invention, step (c) comprises increasing the temperature of the amorphous, paramagnetic or anti-paramagnetic layer to up to the melting point of the at least one component thereof, e.g., by irradiating the layer with photons or energetic particles at the selected locations, such as by photon irradiation utilizing a focussed laser or a focussed, high-intensity lamp as a photon source, or by utilizing an electron beam source as a source of energetic particles.
According to still further embodiments of the present invention, step (c) comprises scanning the photons or energetic particles across the surface of tile amorphous, paramagnetic or anti-paramagnetic layer to impinge at the selected locations thereof, or irradiating the photons or energetic particles through an aperture-patterned mask having a plurality of openings therethrough with predetermined dimensions corresponding to a preselected size of the at least partially crystalline, ferromagnetic particles or grains; the pattern being two-dimensional and defining a checkerboard or other shape pattern of the at least partially crystallized, ferromagnetic particles or grains surrounded by the amorphous, paramagnetic or anti-paramagnetic layer.
According to further exemplary embodiments of the present invention:
step (a) comprises providing a non-magnetic, disk-shaped substrate comprising a material selected from the group consisting of metals, metal alloys, aluminum (Al), Al-based alloys, ceramics, glasses, polymers, and composites thereof;
step (b) comprises forming a layer of amorphous nickel-phosphorus (Nixe2x80x94P) as the amorphous, paramagnetic or anti-paramagnetic material; and
step (c) comprises increasing the temperature of the amorphous Nixe2x80x94P layer at the selected locations to a temperature, e.g., up to about 350xc2x0 C., for an interval sufficient to form and at least partially crystallize ferromagnetic Ni particles or grains thereat.
According to another aspect of the present invention, a high areal storage density, patterned magnetic data/information recording, storage and retrieval medium comprises:
a non-magnetic substrate having a surface: and
a patterned magnetic layer on the substrate surface, the patterned magnetic layer comprising a plurality of spaced-apart, at least partially crystalline, ferromagnetic particles or grains surrounded by a matrix of an amorphous, paramagnetic or anti-paramagnetic material.
According to embodiments of the present invention, the non-magnetic substrate comprises a material selected from the group consisting of metals, metal alloys, aluminum (Al), Al-based alloys, ceramics, glasses, polymers, and composites thereof; and the patterned magnetic layer comprises a plurality of spaced-apart, at least partially crystalline, ferromagnetic particles or grains comprising at least one metal element which is ferromagnetic when in at least partially crystalline form, selected from the group of metal elements consisting of iron (Fe), nickel (Ni), and cobalt (Co), the particles or grains being surrounded by a matrix comprised of a metal glass paramagnetic or anti-paramagnetic layer including at least one of the aforementioned metal elements.
According to further embodiments of the present invention, the non-magnetic substrate is disk-shaped; and the patterned magnetic layer comprises a plurality of spaced-apart, at least partially crystalline, ferromagnetic Ni particles or grains surrounded by a matrix of amorphous Nixe2x80x94P.
According to still further embodiments of the present invention, the patterned magnetic layer comprises a two-dimensional, checkerboard pattern of at least partially crystalline, ferromagnetic particles or grains and a surrounding matrix of amorphous, paramagnetic or anti-paramagnetic material; and the magnetic medium further comprises a protective overcoat layer over the patterned magnetic layer and a lubricant topcoat layer over the protective overcoat layer.
According to yet another aspect of the present invention, a magnetic medium comprises:
a non-magnetic substrate including a surface; and
patterned magnetic means formed within a layer of amorphous material on the substrate surface.
According to an embodiment of the present invention, the patterned magnetic layer means comprises a plurality of spaced-apart, at least partially crystalline, ferromagnetic particles or grains surrounded by a matrix of amorphous, paramagnetic or anti-paramagnetic material comprising at least one component which is ferromagnetic when in at least partially crystalline form.
Additional advantages and aspects of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein embodiments of the present invention are shown and described, simply by way of illustration of the best mode contemplated for practicing the present invention. As will be described, the present invention is capable of other and different embodiments, and its several details are susceptible of modification in various obvious respects, all without departing from the spirit of the present invention. Accordingly, the drawing and description are to be regarded as illustrative in nature, and not limitative.